The present invention relates to a magnetic and reproducing apparatus such as a video tape recorder for domestic use (a household VTR), and more particularly, to a rotational force control mechanism for a reel drive device in the magnetic recording and reproducing apparatus.
Conventionally, as disclosed in Japanese Patent Publication No. 2-10499B (58-53049A), for example, a belt (a rubber belt or the like) having a rectangular cross-section is used for transmission of a rotational force from a capstan motor to a take-up pulley to drive a reel. Little notice is normally taken of controlling the rotational force to be transmitted between the capstan motor and the take-up pulley.
As in the above-described prior art, when a rubber belt is used for power transmission, a reliability of the belt to transmit the power is sometimes lowered due to deterioration of the rubber under long use. In order to solve the problem, a so-called toothed belt which is provided with a number of teeth (projections) has recently been used to transmit the power in order to ensure a reliability over a long period of time.
Here, the toothed belt will be explained more in detail. In the toothed belt, generally, high-strength plastic fibers are provided in a core portion so as to obtain a longtime reliability; a soft material such as urethane resin is coated on an outer side of the belt; and a number of teeth (projections) are provided on an inner side of the belt for the purpose of securely transmitting the power. In case of using the toothed belt, a belt pulley of the capstan motor and the take-up pulley, between which the toothed belt is extended, are formed on their outer peripheries with toothed portions corresponding to the teeth (projections) of the toothed belt. In a rotational force transmitting mechanism utilizing the toothed belt constructed in the above-mentioned manner, if an excessive power is applied between the teeth of the toothed belt and the toothed portions of the pulleys when the capstan motor is rapidly started or stopped or when an extraordinarily large load is applied serious accident such as damage of the teeth of the toothed belt or cutting of the belt may occur.
In order to prevent these accidents, it is known to provide a rotational force control device in the toothed belt rotational force transmitting mechanism. More specifically, in the case where an excessive load over a certain value (allowable value) is applied to the toothed belt rotational force transmitting mechanism, a predetermined portion of the mechanism is designed to race upon application of a predetermined rotational force, to thereby prevent the members of the mechanism from damage. In a conventional rotational force control mechanism, however, as disclosed in the aforementioned Japanese Patent Publication No. 2-10499B (58-53049A), a so-called opposed disk frictional type clutch mechanism is used in which disk-like rotary members are pressed against each other from the outer sides thereof by means of spring members with a frictional member such as a wool felt interposed between the rotary members. This structure involves such disadvantages as to require a number of component parts, to bring about a high cost and to increase the size of the mechanism.
In view of the above-described problems, the present invention aims to provide a magnetic recording and reproducing apparatus including a rotational force control mechanism with a simplified structure which enables reduction in cost and size of the magnetic recording and reproducing apparatus.